1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the zoom lens, and more particularly, though not exclusively, a zoom lens that can be used, for example, in an image pickup apparatus.
2. Description of the Related Art
Recently, a solid-state image sensor that can be used in an image pickup apparatus such as a digital camera has a large number of pixels. In addition, the market has desired that a zoom lens for an image pickup apparatus using an image sensor having a large number of pixels has a specification with which various aberrations occurring with respect to a single color and chromatic aberrations are sufficiently corrected. Particularly, for a zoom lens having a high zoom ratio and a long focal length at the telephoto end, the market has desired to reduce a secondary spectrum in addition to achromatism of a first-order spectrum.
In order to correct chromatic aberration, U.S. Pat. No. 4,913,535 discusses an optical system using a liquid material that has a high degree of dispersion and extraordinary partial dispersion as optical characteristics.
In addition, U.S. Pat. No. 7,088,521 discusses a zoom lens whose chromatic aberration at the telephoto end is corrected and reduced by utilizing dispersion characteristics of an indium tin oxide (ITO) resin that uses an optical element in which ITO particles are dispersed.
In an optical system that uses a liquid material having an achromatic effect, a structure for sealing the liquid material is necessary. Accordingly, manufacture of such an optical system is complicated. In addition, characteristics such as a refractive index and dispersion characteristics vary due to a change in temperature, which makes it difficult to maintain excellent environment tolerance.